1. Comparison Between Diesel Engine and Gasoline Engine
Generally, as compared to gasoline engines (spark-ignition engines), diesel engines (compression-ignition engines) increase thermal efficiency by approximately 30% (20-40% claimed in some references) and reduce green-house effects caused by emissions by approximately 45%. They also have a lower carbon monoxide and HC emission. Diesel engines have simple structures and low failure rate, but have the defect of emitting large harmful particles.
As compared to diesel engines, gasoline engines are different in fuel storage and delivery system. Gasoline is more volatile and wettable. Gasoline engines and diesel engines have different manners in fuel feeding. For gasoline engines, gasoline is injected into air passage and mixed with air before entering into cylinders, while for diesel engines, air is firstly compressed with cylinder pistons and then diesel is injected into cylinders with injection nozzle.
In recent years, there appears a GDI (gasoline direct injection) gasoline engine in market, wherein part of gasoline is pre-injected into cylinders to be pre-blended with air during compression phase, and after piston arrives at the upper dead point, gasoline is injected into cylinders for multiple times, adopting spark plug ignition. This engine uses high rating gasoline, and its compression ratio is fairly improved but not too much. Another Homogeneous Charge Compression Ignition (HCCI) gasoline engines is still under research phase, which may achieve compression-ignition and multi-ignition through pre-injection (premixing gasoline with air) and multiple injection gasoline, appropriately elevating compression ratio and heating with heater plug. Nevertheless, HCCI gasoline engines have problems in combustion controlling and rough operations, and are difficult to be popularized.
As to rough operations of diesel engines: since diesel's kinematic viscosity is rather high, diesel has to be injected into cylinders with high pressure oil pump so as to be sufficiently atomized For achieving a well mixing of diesel with air, this oil pump injection pressure sometimes may reach as high as 1800 to 2000 atmospheric pressure. Therefore, conventional diesel engines generally inject diesel into cylinders within a very short period, so that the atomized diesel spontaneously ignited after mixed with air, causing deflagration by igniting multiple sites at the same time, raising much noise and vibration, hence resulting in rough operations.
Modern diesel engines have already adopted some advanced technologies, such as turbocharging, intercooler, direct injection, catalytic conversion of exhaust gas and particle collection, etc. The emissions of vehicles with diesel engine have met the Euro III, Euro IV and even Euro V emission standards.
2. Engine Compression Ratio and Heat Efficiency
Theoretically, the higher the compression ratio is, the more efficient the engine. The general compression ratio of gasoline engine is 7 to 11, high octane rating (high grade) gasoline needs to be used. The general compression ratio of diesel engine is 15 to 18, and some may reach as high as 18 to 22. Nevertheless, due to the limitation of the strength of cylinders materials, its compression ratio cannot be too high.
3. Specific Fuel Consumption
Fuel consuming rate refers to fuel quantity (based on the unit g) consumed in 1 hour for each 1 kw efficient power the engine produces. Obviously, the lower the fuel consuming rate, the more economic the engine.
4. Aromatic Hydrocarbon and Octane Rating
Gasoline contains xylene, ethylbenzene, toluene, methyl-ethyl benzene or other benzene derivatives, which are all named aromatic hydrocarbon. Aromatic hydrocarbon generally has a high octane rating, but is slightly toxic. The exhaust gas produced by the combustion of aromatic hydrocarbon contains PAHs, which will cause cancer.
In order to increase gasoline's octane rating, refineries generally adopt “reforming” process, converting straight-chain alkanes into aromatic hydrocarbon. This process consumes a large amount of energy and wastes part of the raw materials.
5. Antiknock Agents
To increase gasoline octane rating, engineers have also developed antiknock agents, e.g., methyl cyclopentadienyl manganese tricarbonyl (MMT), methyl tert-butyl ether (MTBE), TAME, etc. Use of MMT and MTBE often causes secondary contamination to the environment. MTBE is prohibited in some states in US by regulations.
6. Octane Rating and Cetane Value
Among the quality indexes of diesel, cetane value is a primary index determining whether diesel can be compressively ignited. Generally, diesel should have a cetane value of 40 to 60, and the higher the cetane value, the easier diesel engines can be compressively ignited. Research shows that a cetane value of 40 is equivalent to an octane rating of 50, and a cetane value of 60 is equivalent to an octane rating of 30. As a matter of fact, the lower the gasoline octane rating is, the easier it can be compressively ignited.
7. Novel Engine With Diesel Engine Advantages in Combination With Gasoline Engine Advantages
Diesel engine has a heat efficiency higher than gasoline engine, mainly because it has a higher compression ratio and a higher air-fuel ratio. Gasoline has a better volatility than diesel, and a better air-mixing homogeneity than diesel. The carbon black particle impurity left in the exhaust gas is less than diesel.
The present invention designs a compression-ignition gasoline engine with high compression ratio. And this novel internal combustion engine has so far not been reported yet.
Reference to the details of the FIG. 1 is provided as below: 1. low octane rating gasoline; 2. fuel tank; 3. fuel pump; 4. fuel pipe; 5. fuel pipe; 6. fuel filter of gasoline; 7. high pressure fuel pump; 8. high pressure fuel rail; 9. high pressure fuel pipe; 10. spray nozzle; 11. valve; 12. combustion chamber; 13. cylinder; 14. piston; 15. connecting rod; 16. crankshaft; 17. lubricating oil system.